Aberration correction device, aberration correction method and optical pickup

ABSTRACT

The present invention is to provide an improved aberration correction device formed by inserting an electro-optic panel such as a liquid crystal panel in an image-formation optical system to correct aberrations in the image-formation optical system, characterized in that such a correction device is capable of correcting three or more kinds of aberrations using only one electro-optic panel. 
     Divided areas concerning coma aberration correction and divided areas concerning astigmatism correction are formed in one of the transparent electrodes of the electro-optic panel, while the rest of divided areas concerning coma aberration correction and divided areas concerning spherical aberration correction are formed in the other of the transparent electrodes. In this way, it is possible to form divided areas divided into electrode patterns suitable for correcting various aberrations, simplify as much as possible the electrode structure of the transparent electrodes consisting of the divided areas, thereby simplifying a control of voltages to be applied to the divided areas.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Stage entry of International ApplicationNo. PCT/JP2005/007218 filed Apr. 14, 2005, which claims benefit of JapanApplication No. 2004-133844 filed Apr. 28, 2004, the entirespecification claims and drawings of which are incorporated herewith byreference.

TECHNICAL FIELD

The present invention relates to an aberration correction device, anaberration correction method and an optical pickup.

BACKGROUND TECHNIQUE

Conventionally, to dynamically correct aberration in an image-formationoptical system, there has been known an aberration correction deviceusing a liquid crystal panel. Such an aberration correction device isfabricated in a manner such that transparent electrodes of its liquidcrystal panel are formed by virtue of divided areas having aberrationcorrection patterns, and aberration correction is performed by providinga phase difference corresponding to a divided area to a light beampassing through the liquid crystal panel, by virtue of an electro-opticeffect of the liquid crystal panel.

Such an aberration correction device is used in an image-formationoptical system of an optical pickup which converges a light beam emittedfrom a light source on to a recording surface of an optical informationrecording medium, while a reflection light from the recording surface isformed into an image on a detection surface of a detector. In such animage-formation optical system, a coma aberration occurred due to a tiltor the like of an optical information recording medium, a sphericalaberration occurred due to a thickness error of an optical recordingmedium, an astigmatism occurred due to distortion of optical parts ofthe optical pickup will each bring about a significant unfavorableinfluence on a recording/reproducing performance. As a result, theforegoing three kinds of aberrations have become correction objects foran aberration correction device to deal with. In using theabove-described aberration correction device having a liquid crystalpanel, when an aberration correction is performed, it is required tofind a wave surface aberration distribution of each aberration in apupil surface of an objective lens, so as to form an electrode patternconsisting of divided areas in transparent electrode of the liquidcrystal panel inserted in an image-formation optical system, in responseto the wave surface aberration distribution.

For example, the following patent document 1 has disclosed an opticalpickup having a laser light source, an objective lens, and an aberrationcorrection means consisting of a liquid crystal panel provided on anoptical axis of a laser beam. In such an optical pickup, one transparentelectrode of the liquid crystal panel consisting of a pair oftransparent electrodes is used as a first electrode divided into apattern corresponding to a wave surface aberration distribution of acoma aberration in a pupil surface of an objective lens, while the othertransparent electrode is used as a second electrode divided into apattern having a converging function for correcting a sphericalaberration.

Moreover, the patent document 1 has disclosed that one electrode of apair of transparent electrodes in the liquid crystal panel forming anaberration correction means is divided into a pattern corresponding to awave surface aberration distribution of a coma aberration in a pupilsurface of the objective lens, as well as a pattern for correcting aspherical aberration.

The following patent document 2 has disclosed another aberrationcorrection device using a similar liquid crystal panel, in which a lightbeam passing area of the liquid panel is divided into a plurality ofportions corresponding to an astigmatism distribution, while voltagescorresponding to the directions of the astigmatisms to be corrected areapplied to the electrodes provided in the divided areas, and a phasedifference for correcting an astigmatism is provided to a light beampassing through each divided area in response to a voltage change.

Patent document 1: Japanese Unexamined Patent Application PublicationNo. (Hei) 10-289465.

Patent document 2: Japanese Unexamined Patent Application PublicationNo. 2000-40249.

DISCLOSURE OF THE INVENTION Problem(s) to be Solved by the Invention

When several kinds of aberrations need to be corrected as in theabove-discussed image-formation optical system, if an aberrationcorrection is performed using an electro-optic effect of theaforementioned liquid crystal panel, once divided areas of an electrodepattern for correcting different aberrations are formed in a pair oftransparent electrodes of the liquid crystal panel, it is allowed tocorrect only two kinds of aberrations.

Moreover, as disclosed in patent document 1, when one transparentelectrode in a liquid crystal panel consisting of a pair of transparentelectrodes is divided to satisfy two kinds of aberration corrections, itwould be impossible to form divided areas suitable for two kinds ofaberration. For example, as discussed in patent document 1, a circulardivided area having a converging function for correcting a sphericalaberration is divided into three portions in a predicted tilt directionof an optical information recording medium as well as in a directionperpendicular to the predicted tilt direction, thereby forming on onetransparent electrode side a divided area concerning coma aberrationcorrection and another divided area concerning spherical aberrationcorrection. In this way, if a circular divided area having a convergingfunction is set at a size capable of correcting a spherical aberration,it would be impossible to form a divided area capable of effectivelycorrecting a coma aberration. On the other hand, if a circular dividedarea is set at a size capable of correcting a coma aberration, it wouldbe impossible for such a size to ensure an appropriate convergingfunction for correcting aspherical aberration. As a result, there hasbeen a problem that once one kind of aberration correction is to beensured, the performance of the other kind of aberration correction willbecome deteriorated.

Moreover, it is also considerable to form divided areas necessary for aplurality of aberration corrections by forming finely divided electrodepatterns on at least one transparent electrode side and then combiningtogether these fine electrode patterns. This, however, makes electrodestructure complex, rendering it difficult to control some portions wheremutual interference occur due to corrections of different aberrations.

The present invention is to deal with the above-discussed problem andmakes this as one of its tasks. Namely, the present invention is toprovide an improved aberration correction device formed by inserting anelectro-optic panel such as a liquid crystal panel in an image-formationoptical system to correct aberrations in the image-formation opticalsystem. Such an improved correction device is capable of correctingthree or more kinds of aberrations using only one electro-optic panel,forming, on a pair of transparent electrodes of the electro-optic panel,divided areas divided into electrode patterns suitable for correctingvarious aberrations, simplifying as much as possible a structure of thetransparent electrodes consisting of the divided areas, therebysimplifying a control of voltage applied to the divided areas.

Means for Solving the Problem

In order to achieve the foregoing object, an aberration correctiondevice, an aberration correction method and an optical pickup accordingto the present invention have at least the following features recited inthe following independent claims.

[Claim 1] There is provided an aberration correction device in which anelectro-optic panel is inserted into an image-formation optical systemto perform aberration correction in the image-formation optical system.In particular, the electro-optic panel comprises a pair of transparentelectrodes which are formed by virtue of divided areas divided intoelectrode patterns capable of correcting several kinds of aberrations.Furthermore, part of the divided areas concerning one kind of aberrationcorrection are formed in one of the transparent electrodes, and the restof the divided areas concerning the one kind of aberration correctionare formed in the other of the transparent electrodes.

[Claim 4] There is provided another aberration correction device formedby inserting an electro-optic panel into an image-formation opticalsystem of an optical pickup to correct aberrations in theimage-formation optical system, the optical pickup being a device inwhich a light beam emitted from a light source is converged on to arecording surface of an optical information recording medium and areflection light from the recording surface is formed into an image on adetection surface of a detector. In particular, the electro-optic panelcomprises a pair of transparent electrodes which are formed by virtue ofdivided areas divided into electrode patterns capable of correctingseveral kinds of aberrations. Furthermore, part of the divided areasconcerning coma aberration correction and divided areas concerningastigmatism correction are formed in one of the transparent electrodes,while the rest of the divided areas concerning coma aberrationcorrection and divided areas concerning spherical aberration correctionare formed in the other of the transparent electrodes.

[Claim 5] There is provided an aberration correction method in which anelectro-optic panel is inserted into an image-formation optical systemof an optical pickup to correct aberrations in the image-formationoptical system, the optical pickup being a device in which a light beamemitted from a light source is converged onto a recording surface of anoptical information recording medium and a reflection light from therecording surface is formed into an image on a detection surface of adetector. In particular, the electro-optic panel comprises a pair oftransparent electrodes which are formed by virtue of divided areasdivided into electrode patterns capable of correcting several kinds ofaberrations. Furthermore, at least at a time of correcting comaaberration, one voltage is applied to part of divided areas concerningcoma aberration correction and formed in one of the pair of thetransparent electrodes, while another voltage is applied to the rest ofthe divided areas concerning coma aberration correction and formed inthe other of the transparent electrodes.

[Claim 6] There is provided an optical pickup having an image-formationoptical system in which a light beam emitted from a light source isconverged on to a recording surface of an optical information recordingmedium and a reflection light from the recording surface is formed intoan image on a detection surface of a detector. In particular, anelectro-optic panel for correcting aberrations in the image-formationoptical system is inserted into an image-formation optical system.Furthermore, the electro-optic panel comprises a pair of transparentelectrodes which are formed by virtue of divided areas divided intoelectrode patterns capable of correcting several kinds of aberrations,part of the divided areas concerning coma aberration correction anddivided areas concerning astigmatism correction are formed in one of thetransparent electrodes, while the rest of the divided areas concerningcoma aberration correction and divided areas concerning sphericalaberration correction are formed in the other of the transparentelectrodes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view showing an example of a structure of anoptical pickup having an aberration correction device formed accordingto one embodiment of the present invention.

FIG. 2 is an explanatory view showing a structure of a liquid crystalpanel (electro-optic panel) according to an embodiment of the presentinvention.

FIG. 3 is an explanatory view showing a distribution of coma aberration.

FIG. 4 is an explanatory view showing an electrode pattern concerningcorrection of coma aberration.

FIG. 5 is an explanatory view showing a distribution of astigmatism.

FIG. 6 is an explanatory view showing an electrode pattern concerningcorrection of astigmatism.

FIG. 7 is an explanatory view showing a distribution of sphericalaberration.

FIG. 8 is an explanatory view showing an electrode pattern concerningcorrection of spherical aberration.

FIG. 9 is an explanatory view showing electrode pattern of an aberrationcorrection device according to an embodiment of the present invention.

FIG. 10 is an explanatory view showing voltage applying pattern of anaberration correction device according to an embodiment of the presentinvention.

FIG. 11 is a block diagram showing an example of an internal structureof a drive/control unit for driving and controlling a liquid crystalpanel (electro-optic panel) according to an embodiment of the presentinvention.

FIG. 12 is an explanatory graph explaining a voltage-phasecharacteristic of a liquid crystal panel.

FIG. 13 shows comparative examples explaining an aberration correctionperformance of the aberration correction device according to anembodiment of the present invention.

FIG. 14 is a graph explaining an aberration correction performance ofthe aberration correction device according to an embodiment of thepresent invention.

BEST MODE OF CARRYING OUT THE INVENTION

Next, description will be given to explain embodiments of the presentinvention with reference to the accompanying drawings. However, sincethe aberration correction device and the aberration correction methodaccording to the embodiments of the present invention are suitable to beused with an optical pickup, the following description will be based onexamples of their applications to an optical pickup. On the other hand,the aberration correction device and the aberration correction methodaccording to the embodiments of the present invention are by no means tobe limited to these examples. Moreover, although the followingdescription will be based on a liquid crystal panel which serves as anexample of an electro-optic panel of an aberration correction device,the electro-optic panel according to the present invention should not belimited to liquid crystal panel, provided that the electro-optic panelis comprised of a pair of transparent electrodes, capable of effectingan adjustment in phase difference of a transmitting light beam by virtueof a voltage applied to transparent electrodes.

FIG. 1 is an explanatory view showing an example of a structure of anoptical pickup having an aberration correction device formed accordingto one embodiment of the present invention. As shown, the optical pickuphas an image-formation optical system (including an object lens 4A, acollimator lens 4B, converging lens 4C) which converges a light beam L₁emitted from a light source 1 such as red color (wavelength: 650 nm) LD(Laser Diode) on to a recording surface 2 a of an optical informationrecording medium 2 such as an optical disc, thereby forming a reflectionlight L₂ from the recording surface 2 a into an image on a detectionsurface 3 a of a detector 3. The optical pickup further comprises apolarization beam splitter 5 for dividing the emitted light beam L₁ andthe reflection light L₂, and ¼λ wave length plate 6. Besides, ifnecessary, the optical pickup has an upright prism 7 for effecting anoptical-path polarization.

Here, the linearly polarized light beam L₁ transmitting through thepolarization beam splitter 5 passes through the ¼λ wave length plate 6intersected with a polarized wave surface of the linearly polarizedlight at an angle of 45 degrees, thereby forming a circularly polarizedlight which is converged by the objective lens 4A and reflected by therecording surface 2 a, thus forming a reflection light L₂ which againpasses through the ¼λ wavelength plate 6 to form a linearly polarizedlight which arrives at the polarization beam splitter 5. At this time,since the polarization axis of the reflection light L₂ becomes 90degrees with respect to the polarization axis of the light beam L₁, thereflection light L₂ is reflected by the polarization beam splitter 5 andtravels towards the detector 3.

The liquid crystal panel (electro-optic panel) 10 which performsaberration correction in the image-formation optical system is insertedinto the image-formation optical system of the optical pickup. Further,there is provided a driving/control unit 8 for driving and controllingthe liquid crystal panel 10. In this way, it is possible to control avoltage applied to the liquid crystal panel 10 in response to an outputfrom the detector 3 (or an output from a tilt sensor which detects atilt of an optical information recording medium).

FIG. 2 is an explanatory view showing a structure of a liquid crystalpanel 100 according to an embodiment of the present invention. As shown,the liquid crystal panel 10 comprises at least a pair of transparentelectrodes 12 a, 12 b. In more detail, a pair of transparent electrodes12 a, 12 b are formed on mutually facing surfaces of a pair oftransparent substrates 11 a, 11 b. Further, orientation films 13 a, 13 bfor providing a predetermined molecular orientation to the liquidcrystal molecules M are formed on the mutually facing surfaces, followedby sealing a liquid crystal layer 14 having double refractions such asnematic liquid crystal between the orientation films 13 a, 13 b.

The aberrations in the image-formation optical system of such an opticalpickup, as described above, are three kinds of aberrations including acoma aberration caused due to a tilt or the like of an opticalinformation recording medium 2, a spherical aberration caused due to athickness error or the like of the optical information recording medium2, and an astigmatism occurred due to distortion of optical parts of theoptical pickup.

FIG. 3 shows a distribution of coma aberration. As shown, thedistribution of coma aberration is represented by values on a pupilsurface of the objective lens 4. An aberration distribution at anoptimum image point of a converged spot of the light beam L₁ when theoptical information recording medium 2 is tilted +10° is shown in arange of an open pupil 4A₀ of the objective lens 4A (maximum area of thelight beam L₁) (showing board lines of various areas A-K in a range of50 nm with an area A having an aberration value of −25 nm to +25 nmserving as a center). Here, X₂-X₂ is an axis corresponding to adirection in which the optical information recording medium 2 tilts.

Paying attention to the distribution of such a coma aberration, anelectrode pattern formed in the transparent electrode 12 a (12 b) of theliquid crystal panel 10 can form divided areas consisting of shapesalong the aberration distribution shown in FIG. 3. Further, it ispossible to provide a phase difference to a light beam to eliminate anaberration occurred in each divided area by virtue of a voltage appliedto the divided area.

FIG. 4 shows an electrode pattern. As shown, an electrode patternsuitable for correcting coma aberration consists of five divided areasE_(C0)-E_(C4) (4A₀ is an open pupil of an objective lens) Here, adivided area E_(C0) is an area whose aberration value is 0, dividedareas E_(C0) and E_(C4) are areas corresponding to an aberrationindicating a large absolute value on the positive (+) side, dividedareas E_(C2) and E_(C3) are areas corresponding to an aberrationindicating a large absolute value on the minus (−) side. In this way, ifa voltage having a reversed polarity is applied to the divided areasE_(C1), E_(C4) and divided areas E_(C2), E_(C3), and if a phasedifference is provided to the light beam to eliminate aberration, it ispossible to correct a coma aberration.

FIGS. 5( a)-5(c) shows an astigmatism distribution in the pupil surfaceof the objective lens 4A. FIG. 5( a) shows an astigmatism distributionsurrounding an optical axis, with dark portions representing areashaving large astigmatism. FIGS. 5( b) and 5(c) show Y1 a-Y1 b sectionand X1 a-X1 b section in FIG. 5( a). The astigmatism distribution in thepupil surface of the objective lens 4A is formed in a manner such thatan aberration amount is larger closer to edge with X1 a-X1 b axis and Y1a-Y1 b axis serving as objects, and that an aberration amount is smallat an angle of 45° between X1 a-X1 b axis and Y1 a-Y1 b axis. In fact,such an astigmatism distribution is not a characteristic of eachimage-formation optical system, while an optical system involvingastigmatism has the same distribution pattern. However, its directionwill be different depending on different optical system, with the X1a-X1 b axis and Y1 a-Y1 b axis of FIG. 5( a) rotating by virtue of theoptical system. Further, an aberration amount and its direction of theastigmatism will also have different values depending on differentoptical system.

Paying attention to such an astigmatism distribution, an electrodepattern formed in transparent electrode 12 a (12 b) of the liquidcrystal panel 10 can form the divided areas consisting of shapes alongthe aberration distribution shown in FIG. 5. Further, it is possible toprovide a phase difference to a light beam to eliminate an aberrationoccurred in each divided area by virtue of a voltage applied to thedivided area.

FIG. 6 shows an electrode pattern. As shown, an electrode patternsuitable for correcting astigmatism has for example nine divided areasE_(AS0)-E_(AS8) with respect to an open pupil 4A₀ of the objective lens4A. One divided area E_(AS0) is a circular pattern corresponding to acentral portion of the open pupil 4A₀, while other divided areasE_(AS1)-E_(AS8) are patterns radially divided in the perimeter portionand symmetrically arranged in a manner such that they are separated fromone another at substantially the same interval and the same angle fromthe center of the open pupil 4A₀. Then, the divided areas E_(AS1),E_(AS5), E_(AS2) and E_(AS6), E_(AS3) and E_(AS7,) E_(AS4), E_(AS8) arearranged to face one another and positioned centrally symmetrically,while voltages having the same polarity are selectively applied to theseareas, thereby making it possible to perform an aberration correctioncorresponding to a specific direction of an astigmatism.

FIG. 7 shows a distribution of a spherical aberration in the pupilsurface of the objective lens 4A. Such a spherical aberration shows asymmetrical distribution with respect to the center O of the open pupil4A₀, with an aberration amount being zero at the center O and along theedges of the open pupil 4A₀, and becoming large in an annular areaslightly separated from the center O.

FIG. 8 shows an electrode pattern which enables correction of thespherical aberration. As shown, such electrode pattern forms dividedareas consisting of shapes corresponding to an aberration distributionshown in FIG. 7. Further, it is possible to provide a phase differenceto a light beam to eliminate an aberration occurred in each divided areaby virtue of a voltage applied to the divided area. Namely, the dividedareas at this time include a circular divided area E_(SA0) correspondingto central portion of the open pupil 4A₀ of the objective lens 4A, anannular divided perimeter area E_(SA1), and a divided area E_(SA2) inthe perimeter portion.

Using the liquid crystal panel 10 of the aberration correction deviceaccording to the present invention, it is possible to effectivelycorrect three kinds of aberrations (coma aberration, astigmatism,spherical aberration) by virtue of one liquid crystal panel 10.Therefore, it is possible to form part of the divided areas concerningone kind of aberration correction in one of the transparent electrodes12 a and 12 b, and the rest of the divided areas concerning this onekind of aberration correction in the other of the transparent electrodes12 a and 12 b.

FIGS. 9( a) and 9(b) show in more detail electrode patterns of thetransparent electrodes 12 a, 12 b. Here, FIG. 9( a) shows an electrodepattern of one of the transparent electrodes 12 a, 12 b, while FIG. 9(b) shows an electrode pattern of the other of the transparent electrodes12 a, 12 b.

In the electrode pattern shown in FIG. 9 (a) there are formed part ofdivided areas concerning coma aberration correction and divided areasconcerning astigmatism correction. Namely, a generally circular patternE₀ is formed in the center of the open pupil 4A₀ of the objective lens4. This is then divided into three portions E₀₀, E₀₁, and E₀₂ to formpart of divided areas concerning coma aberration correction, while edgeportion on the outside of the generally circular pattern E₀ is radiallydivided to form divided areas E₁₁-E₁₈ concerning astigmatism correction.

At this time, the generally circular pattern E₀ and the divided areasE₀₀, E₀₁, and E₀₂ are set to ensure a pattern effective in aberrationcorrection, in accordance with an aberration distribution of comaaberration shown in FIG. 3. Then, the perimeter portion is divided atsubstantially an equal angle from the center of the open pupil 4A₀ so asto set symmetrically divided areas E₁₁-E₁₈, with the divided areas E₁₁and E₁₅, E₁₂ and E₁₆, E₁₃ and E₁₇, E₁₄ and E₁₈ respectively facing eachother and arranged in a centrally symmetric array.

Moreover, in an electrode pattern shown in FIG. 9( b) there are formeddivided areas concerning coma aberration correction and divided areasconcerning spherical aberration correction. Namely, the divided areasconcerning spherical aberration correction include a circularlypatterned divided area E₂₀ formed in the center of the open pupil 4A₀ ofthe objective lens 4, and an annular concentrically patterned dividedarea E₂₁. Further, the rest of divided areas (E₃₁, E₃₂, E_(30a),E_(30b)) concerning coma aberration correction are formed on the outsideof the annular area.

At this time, the circularly patterned divided area E₂₀ and the annularconcentrically patterned divided area E₂₁ are set to be suitable forcorrecting spherical aberration, while the perimeter area is set as therest of the divided areas (E₃₁, E₃₂, E_(30a), E_(30b)) concerning comaaberration correction.

By virtue of the electrode patterns with respect to the foregoingtransparent electrodes 12 a and 12 b, the divided areas E₀₀, E₀₁, E₀₂,E₃₁, E₃₂, E_(30a), E_(30b) concerning coma aberration correction can bedivided into two groups, with the divided areas E₀₀, E₀₁, E₀₂ beingformed on one of the transparent electrodes 12 a and 12 b, and thedivided areas E₃₁, E₃₂, E_(30a), E_(30b) being formed on the other ofthe transparent electrodes 12 a and 12 b. In this way, all divided areasnecessary for correcting three kinds of aberrations can be formed intopatterns capable of providing the same correction effect as the dividedareas when individually correcting an aberration, without causing anymutual interference among these divided areas.

FIG. 10 shows several voltage patterns applied to the liquid crystalpanel 10 according to the above-described embodiment. FIG. 10( a) showsa voltage pattern applied when correcting a coma aberration, FIG. 10( b)shows a voltage pattern applied when correcting a spherical aberration,FIG. 10( c) shows a voltage pattern applied when correcting anastigmatism.

As shown in FIG. 10( a), voltages are applied to the foregoing dividedareas E₀₁, E₀₂, E₃₁, E₃₂ when correcting coma aberration, with the areasE₀₁ and E₃₂ receiving voltages of the same polarity and the areas E₀₂,E₃₁ receiving voltages of the opposite polarity. As shown in FIG. 10(b), when correcting a spherical aberration, a voltage is applied to theforegoing divided area E₂₁. As shown in FIG. 10( c), when correctingastigmatism, voltages are selectively applied to the divided areas E₁₂,E₁₄, E₁₅, and E₁₈.

FIG. 11 shows an example of a structure of the drive/control section 8which drives/controls the foregoing liquid crystal panel 10. As shown,the drive/control section 8 comprises a controller 80 consisting of CPUwhich receives reproduction signals (RF, PushPull, LPP, or the like)from a detector 3; a memory 81 for storing a bias voltage, anastigmatism direction, an astigmatism amount or the like; a bias voltagegenerating unit 82 for outputting a bias voltage in accordance with anoutput of the controller 80; a coma aberration correction controlvoltage generating unit 83 which outputs a coma aberration correctioncontrol voltage in accordance with an output from the controller 80; anastigmatism correction control voltage generating unit 84 which outputsan astigmatism correction control voltage in accordance with an outputfrom the controller 80; a spherical aberration correction controlvoltage generating unit 85 which outputs a spherical aberrationcorrection control voltage in accordance with an output from thecontroller 80; a bias addition unit 86 which adds a bias voltageoutputted from the bias voltage generating unit 82 to an output from thecoma aberration correction control voltage generating unit 83 as well asto an output from the astigmatism correction control voltage generatingunit 84; and a liquid crystal driving unit 87.

The outputs from the coma aberration correction control voltagegenerating unit 83 and the astigmatism correction control voltagegenerating unit 84 in both of which bias voltages have been added, aresupplied through the liquid crystal driving unit 87 to the divided areas(E₀₀, E₀₁, E₀₂, E₁₁, E₁₅ and E₁₂, E₁₆ and E₁₃, and E₁₇, E₁₄ and E₁₈)formed in one of the pair of transparent electrodes 12 a and 12 b. Onthe other hand, the outputs from the coma aberration correction controlvoltage generating unit 83 and the spherical aberration correctioncontrol voltage generating unit 85 in both of which bias voltages havenot been added, are supplied to the divided areas (E₂₁, E₃₂, E₃₁, E₂₀)formed in the other of the pair of transparent electrodes 12 a and 12 b.Moreover, the divided area E₂₀ is in an earthed state.

Next, description will be given to an operation of the drive/controlsection 8.

At first, regarding an addition of bias voltage, it can be understoodfrom FIG. 12 that a voltage-phase difference characteristic of theliquid crystal panel 10 is limited to an operation range (dynamic range)which can be considered as a linear approximation. Therefore, withregard to coma aberration correction and astigmatism correction whichrequire an amount control or a bipolarity (+, −) control, a bias voltageVc is set in the vicinity of the center of the dynamic range and will bestored in the memory 81. Then, if a phase-difference at a time ofapplying a bias voltage Vc is used as a reference phase difference φc,it is possible to control a positive phase difference (φa−φc) by virtueof a control voltage Va which is higher than the bias voltage Vc, andalso possible to control a negative phase difference (φb−φc) by virtueof a control voltage Vb which is lower than the bias voltage Vc.

Regarding coma aberration correction, a coma aberration at this time iscaused due to a tilt or warp of an optical information recording medium(optical disc) 2 or the like. Such coma aberration correction isperformed in accordance with a magnitude of reproduction signal, ajitter, an error rate, or the like when playing back an opticalinformation recording medium 2 using an optical pickup. In more detail,when the controller 80 sets a coma aberration correction control voltagein accordance with a signal from the detector 3, it will set a comaaberration correction control voltage in a manner such that theamplitude of a tracking error signal or a wobble signal reproduced byapplying a focus servo to the optical information recording medium 2will become maximum.

A control voltage formed by adding the foregoing bias voltage Vc to thecoma aberration correction control voltage is applied to the dividedareas E₀₁ and E₀₂ formed in one of the transparent electrodes 12 a and12 b. On the other hand, since the bias voltage Vc is applied to one ofthe transparent electrodes 12 a and 12 b, a coma aberration correctioncontrol voltage not containing the bias voltage Vc is applied to thedivided areas E₃₁ and E₃₂ formed in the other of the transparentelectrodes 12 a and 12 b.

Next, regarding an astigmatism correction, such astigmatism is mainly anaberration caused due to an insufficient precision in parts or aninadequate assembling precision of an optical pickup. In assembling anoptical pickup, such a correction is performed by observing a beam spotconverged by the objective lens 4A. Once there is astigmatism, a beamspot which should be converged into a circular shape will become anellipse. Accordingly, this is observed, and an ellipse direction as wellas a deformation extent are found, thereby measuring an astigmatismdirection and an astigmatism magnitude which are then stored in thememory 81. In fact, with respect to the beam spot deformed into anellipse, voltages are selectively applied to the divided areas E₁₁-E₁₈and an adjustment is performed in a manner such that the beam spotbecomes circular, with an adjustment value being stored in the memory.

Then, an astigmatism correction at the time of driving an optical pickupcan be carried out as follows. Namely, the controller 80 reads out theabove-mentioned adjustment value from the memory 81 and then suppliesthe value to the astigmatism correction control voltage generating unit84, thereby generating a correction control voltage. Subsequently,another control voltage formed by adding the foregoing bias voltage Vcin the correction control voltage is selectively applied to the dividedareas E₁₁-E₁₈ (one or more pairs of E₁₁ and E₁₅, E₁₂ and E₁₆, E₁₃ andE₁₇, E₁₄ and E₁₈) formed in one of the transparent electrodes 12 a and12 b.

Next, regarding spherical aberration correction, such sphericalaberration is caused due to a thickness error of a covering layer of theoptical information recording medium 2. The spherical aberrationcorrection is carried out in accordance with a magnitude of areproduction signal, a jitter, an error rate or the like when playingback an optical information recording medium 2 using an optical pickup.In more detail, when the controller 80 sets a spherical aberrationcorrection control voltage in accordance with a signal from the detector3, it will set a spherical aberration correction control voltage in amanner such that the amplitude of a tracking error signal or a wobblesignal reproduced by applying a focus servo to the optical informationrecording medium 2 will become maximum. Then, the spherical aberrationcorrection control voltage (not containing the bias voltage Vc) isapplied to the divided area E₂₁ formed in the other of the transparentelectrodes 12 a and 12 b. In this way, since such a voltage applicationprovides a phase difference to a light beam passing through the dividedarea E₂₁, a spherical aberration can thus be corrected.

Next, description will be given to explain an aberration correctionperformance of an aberration correction device formed according to anembodiment of the present invention. FIG. 13 shows comparative examplesexplaining the aberration correction performance of aberrationcorrection device. In the comparative examples, electrode patternsconcerning coma aberration correction are set only in the divided areasE₀₁ and E₀₂, and thus formed only on one of the transparent electrodes.FIG. 14 is a graph showing amounts of wave surface aberrations (comaaberrations) with respect to a tilt angle (a tilt angle in the radialdirection) of an optical information recording medium 2 (optical disc),in the above-described embodiment (example), comparative example, andno-correction case (amounts of wave surface aberrations are calculatedunder the conditions of: NA of objective lens: 0.67; thickness of disc:0.6 mm; wave length of light source: 660 nm).

As clearly understood in FIG. 14, the aberration correction device ofthe present invention makes it possible to reduce coma aberration by 40%as compared with no-correction case, and to ensure an aberrationcorrection performance higher than the comparative example. Further, asto other kinds of aberrations, the present invention makes it possibleto reduce spherical aberration by 50% and astigmatism by 60%. Namely,the aberration correction device of the present invention makes itpossible to obtain an effect equivalent to a case in which therespective aberration correction electrodes are independently designed.

Finally, the aberration correction device, the aberration correctionmethod, and the optical pickup using the aberration correction device orthe method can be concluded as having the following features.

Firstly, the aberration correction device formed by inserting anelectro-optic panel (liquid crystal panel 10) in an image-formationoptical system to perform aberration corrections in the image-formationoptical system, is characterized in that: the image-formation opticalsystem has a pair of transparent electrodes 12 a and 12 b which areformed by virtue of divided areas divided into electrode patternscapable of correcting several kinds of aberrations; part of the dividedareas for correcting one kind of aberration are formed in one of thetransparent electrodes 12 a and 12 b, while the rest of the dividedareas for correcting the foregoing one kind of aberration are formed inthe other of the transparent electrodes 12 a and 12 b.

In this way, the divided areas for correcting one kind of aberration areclassified into two patterns and formed in different transparentelectrodes 12 a and 12 b, thereby making it possible to avoid aninterference of electrode patterns which would otherwise occur if theelectrode patterns for correcting several kinds of aberrations arecollected in only one of the transparent electrodes 12 a and 12 b.Therefore, even when correcting several kinds of aberrations usingsingle one electro-optic panel, it is still possible to independentlycontrol the divided areas concerning various aberrations using a simpleelectrode pattern, thereby rendering it possible to perform an easydriving of the electro-optic panel and avoid a deterioration of anaberration correction performance.

Secondly, the aberration correction device is characterized in that partof divided areas (E₀₀, E₀₁, E₀₂) concerning coma aberration correctionand the divided areas E₁₁-E₁₈ concerning astigmatism correction areformed in one of the transparent electrodes 12 a and 12 b, while therest of divided areas (E₃₁, E₃₂) concerning coma aberration correctionand the divided areas E₂₀ and E₂₁ concerning spherical aberrationcorrection are formed in the other of the transparent electrodes 12 aand 12 b.

In this way, since part of the divided areas (E₀₀, E₀₁, E₀₂) concerningcoma aberration correction and patterned in the center of the open pupil4A₀, and the divided areas E₁₁-E₁₈ concerning astigmatism correction andradially patterned in the vicinity of the open pupil 4A₀ are all formedin one electrode 12 a (12 _(b)), it is possible to form these dividedareas without any mutual interference. Further, since the divided areasE₂₀, E₂₁ concerning spherical aberration correction and patterned in thecenter of the open pupil 4A₀ and the divided areas (E₃₁, E₃₂) concerningcoma aberration correction and patterned in the vicinity of the openpupil 4A₀ are also formed in one electrode 12 a (12 b), it is similarlypossible to form these divided areas without any mutual interference.Therefore, it is possible to independently form electrode patternsconcerning corrections of coma aberration, astigmatism, and sphericalaberration in single one electro-optic panel, and obtain an aberrationcorrection effect equivalent to a case in which various aberrationcorrection electrodes are independently designed.

In more detail, a generally circular pattern in the center is dividedinto three portions to form divided areas (E₀₀, E₀₁, E₀₂) concerningcoma aberration correction in one of the transparent electrodes 12 a and12 b, while an area on the outside of this generally circular pattern isdivided radially to form divided areas E₁₁-E₁₈ concerning astigmatismcorrection. Meanwhile, the central circular pattern, and divided areasE₂₀ and E₂₁ consisting of an annular pattern concentric with the centralcircular pattern and concerning spherical aberration correction areformed in the other of the transparent electrodes 12 a and 12 b, whilethe rest of divided areas (E₃₁, E₃₂) concerning coma aberrationcorrection are formed on the outside of the divided areas E₂₀ and E₂₁,thereby obtaining the above-described effects.

When the aberration correction device having the above-describedfeatures is used in the image-formation optical system of the opticalpickup in which a light beam emitted from the light source 1 isconverged on to the recording surface 2 a of the optical informationrecording medium 2 and the reflection light from the recording surface 2a is formed into an image on the detection surface of the detector 3, itis possible to correct, using only one electro-optic panel, anaberration caused due to a tilt of the optical information recordingmedium 2, an aberration caused due to a thickness error of the opticalinformation recording medium 2, and an aberration caused due to errorsinvolved in manufacturing parts of the optical pickup. In this way, itis possible to produce an optical pickup capable of highly reliableinformation recording or reproducing, at a low cost and a reduced size.

Moreover, in the aberration correction method using the above-describedaberration correction device, at least when correcting a comaaberration, voltages are applied to the divided areas (E₀₁, E₀₂) formedin one of the pair of the transparent electrodes 12 a and 12 bconcerning coma aberration correction, while other voltages are appliedto the divided areas (E₃₁, E₃₂) formed in the other of the pair of thetransparent electrodes 12 a and 12 b concerning coma aberrationcorrection, thereby making it possible to avoid a complex control, thusenabling a driving of the liquid crystal panel 10 in the same manner asa case in which coma aberration is corrected individually.

1. An aberration correction device in which a liquid crystal panel is inserted into an image-formation optical system to perform aberration correction in the image-formation optical system, wherein the liquid crystal panel comprises a pair of transparent electrodes which are formed by virtue of divided areas divided into electrode patterns capable of selectively correcting several kinds of aberrations including coma aberration, spherical aberration and astigmatism, wherein part of the divided areas concerning coma aberration correction are formed in one of the transparent electrodes, and the rest of the divided areas concerning coma aberration correction are formed in the other of the transparent electrodes, wherein the part of the divided areas concerning coma aberration correction and the divided areas concerning astigmatism correction are formed in one of the transparent electrodes, while the rest of the divided areas concerning coma aberration correction and the divided areas concerning spherical aberration correction are formed in the other of the transparent electrodes, wherein a central and generally circular pattern is divided into three portions to form part of the divided areas concerning coma aberration correction in one of the transparent electrodes, and an area on the outside of said generally circular pattern is radially divided to form divided areas concerning astigmatism correction, while a central circular pattern and divided areas consisting of an annular pattern concentric with the central circular pattern concerning spherical aberration correction are formed in the other of the transparent electrodes, and the rest of the divided areas concerning coma aberration correction are formed on the outside of said divided areas concerning spherical aberration correction.
 2. An aberration correction device formed by inserting a liquid crystal panel into an image-formation optical system of an optical pickup to correct aberrations in the image-formation optical system, said optical pickup being a device in which a light beam emitted from a light source is converged on to a recording surface of an optical information recording medium and a reflection light from the recording surface is formed into an image on a detection surface of a detector, wherein the liquid crystal panel comprises a pair of transparent electrodes which are formed by virtue of divided areas divided into electrode patterns capable of selectively correcting several kinds of aberrations including coma aberration, spherical aberration and astigmatism, wherein part of the divided areas concerning coma aberration correction and the divided areas concerning astigmatism correction are formed in one of the transparent electrodes, while the rest of the divided areas concerning coma aberration correction and divided areas concerning spherical aberration correction are formed in the other of the transparent electrodes, wherein a central and generally circular pattern is divided into three portions to form part of the divided areas concerning coma aberration correction in one of the transparent electrodes and an area on the outside of said generally circular pattern is radially divided to form divided areas concerning astigmatism correction, while a central circular pattern and divided areas consisting of an annular pattern concentric with the central circular pattern concerning spherical aberration correction are formed in the other of the transparent electrodes, and the rest of the divided areas concerning coma aberration correction are formed on the outside of said divided areas concerning spherical aberration correction.
 3. An aberration correction method in which a liquid crystal panel is inserted into an image-formation optical system of an optical pickup to correct aberrations in the image-formation optical system, said optical pickup being a device in which a light beam emitted from a light source is converged on to a recording surface of an optical information recording medium and a reflection light from the recording surface is formed into an image on a detection surface of a detector, wherein the liquid crystal panel comprises a pair of transparent electrodes which are formed by virtue of divided areas divided into electrode patterns capable of selectively correcting several kinds of aberrations including coma aberration, spherical aberration and astigmatism, wherein at least at a time of correcting coma aberration, one voltage is applied to part of divided areas concerning coma aberration correction and formed in one of the pair of the transparent electrodes, while another voltage is applied to the rest of the divided areas concerning coma aberration correction and formed in the other of the transparent electrodes, wherein a central and generally circular pattern is divided into three portions to form part of the divided areas concerning coma aberration correction in one of the transparent electrodes and an area on the outside of said generally circular pattern is radially divided to form divided areas concerning astigmatism correction, while a central circular pattern and divided areas consisting of an annular pattern concentric with the central circular pattern concerning spherical aberration correction are formed in the other of the transparent electrodes, and the rest of the divided areas concerning coma aberration correction are formed on the outside of said divided areas concerning spherical aberration correction.
 4. An optical pickup having an image-formation optical system in which a light beam emitted from a light source is converged on to a recording surface of an optical information recording medium and a reflection light from the recording surface is formed into an image on a detection surface of a detector, wherein a liquid crystal panel for correcting aberrations in the image-formation optical system is inserted into an image-formation optical system, wherein the liquid crystal panel comprises a pair of transparent electrodes which are formed by virtue of divided areas divided into electrode patterns capable of correcting several kinds of aberrations including coma aberration, spherical aberration and astigmatism, part of the divided areas concerning coma aberration correction and the divided areas concerning astigmatism correction are formed in one of the transparent electrodes, while the rest of the divided areas concerning coma aberration correction and the divided areas concerning spherical aberration correction are formed in the other of the transparent electrodes, wherein a central and generally circular pattern is divided into three portions to form part of the divided areas concerning coma aberration correction in one of the transparent electrodes, and an area on the outside of said generally circular pattern is radially divided to form divided areas concerning astigmatism correction while a central circular pattern and divided areas consisting of an annular pattern concentric with the central circular pattern concerning spherical aberration correction are formed in the other of the transparent electrodes and the rest of the divided areas concernin coma aberration correction are formed on the outside of said divided areas concerning spherical aberration correction. 